His doctor says he has a pre-existing arthritic condition in his neck and this is a long-term problem that should not be disabling however. There is no reason for him not to be driving a cab, for instance.

I agree with salerno. Or you could say (with minimum alteration to the original sentence):

His doctor says he has a pre-existing arthritic condition in his neck and this is a long-term problem that should not, however, be disabling. There is no reason for him not to drive a cab, for instance.